Thermal solvents in dry photothermographic systems. Heat processable photosensitive elements can be constructed so that after exposure, they can be processed in a substantially dry state by applying heat. It is known how to develop latent image in a photographic element not containing silver halide wherein organic silver salts are used as a source of silver for image formation and amplification. Such processes are described in U.S. Pat. Nos. 3,429,706 (Shepard et al.) and 3,442,682 (Fukawa et al.). Other dry processing thermographic systems are described in U.S. Pat. Nos. 3,152,904 (Sorenson et al.) and 3,457,075 (Morgan and Shely). A variety of compounds have been proposed as "carriers" or "thermal solvents" or "heat solvents" for such systems, whereby these additives serve as solvents for incorporated developing agents, or otherwise facilitate the resulting development or silver diffusion processes. Acid amides and carbamates have been proposed as such thermal solvents by Henn and Miller (U.S. Pat. No. 3,347,675) and by Yudelson (U.S. Pat. No. 3,438,776). Bojara and de Mauriac (U.S. Pat. No. 3,667,959) disclose the use of nonaqueous polar solvents containing thione, --SO.sub.2 -- and --CO-- groups as thermal solvents and carriers in such photographic elements. Similarly, La Rossa (U.S. Pat. No. 4,168,980) discloses the use of imidazoline-2-thiones as processing addenda in heat developable photographic materials. Takahashi (U.S. Pat. No. 4,927,731) discloses a microencapsulated base activated heat developable photographic polymerization element containing silver halide, a reducing agent, a polymerizable compound, contained in a microcapsule and separate from a base or base precursor. In addition the element contains a sulfonamide compound as a development accelerator.
Thermal solvents for use in substantially dry color photothermographic systems have been disclosed by Komamura et at. (U.S. Pat. No. 4,770,981), Komamura (U.S. Pat. No. 4,948,698), Aomo and Nakamaura (U.S. Pat. No. 4,952,479), and Ohbayashi et al. (U.S. Pat. No. 4,983,502). The terms "heat solvent" and "thermal solvent" in these disclosures refer to a non-hydrolyzable organic material which is a liquid at ambient temperature or a solid at an ambient temperature but melts together with other components at a temperature of heat treatment or below but higher than 40.degree. C. Such solvents may also be solids at temperatures above the thermal processing temperature. Their preferred examples include compounds which can act as a solvent for the developing agent and compounds having a high dielectric constant which accelerate physical development of silver salts. Alkyl and aryl amides are disclosed as "heat solvents" by Komamura et al. (U.S. Pat. No. 4,770,981), and a variety of benzamides have been disclosed as "heat solvents" by Ohbayashi et at. (U.S. Pat. No. 4,983,502). Polyglycols, derivatives of polyethylene oxides, beeswax, monostearin, high dielectric constant compounds having an --SO.sub.2 -- or --CO-- group such as acetamide, ethylcarbamate, urea, methylsulfonamide, polar substances described in U.S. Pat. No. 3,667,959, lactone of 4-hydroxybutanoic acid, methyl anisate, and related compounds are disclosed as thermal solvents in such systems. The role of thermal solvents in these systems is not clear, but it is believed that such thermal solvents promote the diffusion of reactants at the time of thermal development. Masukawa and Koshizuka disclose (U.S. Pat. No. 4,584,267) the use of similar components (such as methyl anisate) as "heat fusers" in thermally developable light-sensitive materials. Baxendale and Wood in the Defensive Publication corresponding to U.S. application Ser. No. 825,478 filed Mar. 17, 1969 disclose water soluble lower-alkyl hydroxybenzoates as preprocessing stabilizers in silver salt heat-developable photographic elements.
Heat developable thermal dye-diffusion transfer systems. Hirai et al. (U.S. Pat. No. 4,590,154) disclose a heat developable color photographic light-sensitive material comprising silver halide, a hydrophilic binder, dye releasing compounds which release mobile dyes, and a sulfonamide compound. The compounds disclosed by Hirai et al. have, except for a very few examples, a very low octanol/water partition coefficient, or clogP value (see below). This system requires only heat to develop the latent image and to produce mobile dyes. However, the mobile dyes are affixed to an image receiving material, which must be wetted with water prior to being contacted with the heat developed donor element. The subsequent dye diffusion transfer to the receiver element is therefore of the conventional wet diffusion type.
Nakamine et al. (U.S. Pat. No. 5,017,454) disclose a heat developable photographic chromogenic system that also utilizes diffusion transfer of dyes to an image receiving (fixing) element. The dye diffusion transfer in actuality requires that the image receiving or fixing element be wetted with water prior to being affixed to the dye donor element. The resulting dye transfer, therefore, is a wet diffusion transfer of the conventional type, not dry thermal dye transfer. Kohno et al. (U.S. Pat. No. 5,032,499) disclose a heat developable photographic chromogenic system that also utilizes diffusion transfer of dyes to an image receiving element. The compounds taught as promoting thermal transfer are, except for one of 60 examples, ortho substituted hydroxybenzamides of very low clogP value (see below).
Hydroxybenzene Derivatives in Aqueous-developable Non-diffusion-transfer Color Photographic Systems. Okonogi et al. (U.S. Pat. No. 4,228,235) disclose 2,6-dialkyl hydroxybenzoates as dye light-fade stabilizers in a integral photographic, or non-diffusion transfer type, element. Hirano et al. (U.S. Pat. No. 4,474,874) disclose 5-substituted pyrogallols with amide, acyl, sulfone, or sulfate groups as color fog preventative agents (interlayer scavengers) in an integral photographic element or in an aqueous alkali color image transfer element. Takahashi et al. (U.S. Pat. No. 5,169,742) disclose phenols with sulfone, amide and ester substituents as interlayer scavengers in a integral photographic element. Waki et al. (U.S. Pat. No. 4,626,494) describes an aqueous alkali activated image transfer element containing coupler solvents including 2-ethylhexyl hydroxybenzoate. Takahashi et al. (European Patent Application No. 276,319)disclose image generating layers incorporating low levels of hydroxybenzoates, salicylates and o-hydroxybenzophenones as dye light-stabilizers. Thirtle and Weissberger (U.S. Pat. No. 2,835,579) disclose aqueously processable color photographic elements that contains 2,4-di-n-alkyl-, 2-n-alkyl-4-n-alkylacyl- or 2-n-alkylacyl-4-n-alkylphenols as solvents for dye forming couplers. Sakai et al. (U.S. Pat. No. 4,774,166) disclose seven classes of materials, including as members of one class, arylsulfonylphenols, arylsulfamoylphenols and arylacylphenols as coupling activity enhancing compounds employed in development processes not containing benzyl alcohol. Ishikawa and Sato (Japanese Kokai No. 62-25754) disclose hydroxybenzoates and salicylates as coupling activity enhancing compounds in color photographic elements. Kimura et at. (U.S. Pat. No. 4,551,422) disclose the incorporation of substituted phenols, including alkylphenols, hydroxybenzoates and acylphenols in color photographic elements as hue shifting addenda.
Physical organic characterization of thermal solvents. Materials, especially those that can be treated as substituent variations on an essential functional group, can be described by a variety of extrathermodynamic parameters that relate their activity, according to some performance measure, to their structure. As a central theme of physical-organic chemistry this approach is described in a number of organic chemistry text books, monographs, review articles and review series. Several parameters are employed here that describe the characteristics of the materials that are useful in the practice of this invention. These are the Hammett sigma (.sigma.) values, which characterize the ability of the ring substituents to effect the electronic nature of the reaction site, the octanol/water partition coefficient as either a substituent parameter or the log of the calculated partition coefficient, clogP, which characterizes the octanol/water partition equilibrium of the entire molecule, the pK.sub.a which measures the tendency of a functional group to lose or gain a proton, as referenced to an aqueous environment, and hydrogen bond donating (HBD) and the hydrogen bond accepting (HBA) character of functional groups.
The Hammett sigma constant, as the seminal member of the family of linear free energy relationships, is described in standard physical organic textbooks such as by T. H. Lowry and K. S. Richardson, "Mechanisms and Theory in Organic Chemistry", 3rd ed., Harper & Row, New York; in monographs such as Shorter, "Correlation Analysis of Organic Reactivity", Research Studies Press, Chichester, Great Britain, 1982 and in specialized series such as Progress in Physical Organic Chemistry. The primary and secondary journal literature contains numerous tabulations of Hammett sigma constants such as Hansch et al., J. Med. Chem., 1973, 16, 1207 and Hansch et al., Chem. Rev., 1991, 91, 165. These Hammett sigma values are well established for meta and para substituents, taken for the description of this invention, as relative to the hydrogen bond donating moiety and not involving any enhanced resonance interactions. The apparent sigma values for ortho substituents are often confounded with steric effects leading to a wide variation in the empirically derived substituent ortho sigma values. For the purposes of this invention we have assumed that the ortho sigma values of substituents are equal to its para sigma value. The sigma value for a thermal solvent is the simple algebraic sum of all of the substituents on an aromatic ring exclusive of any hydrogen bond donating substituent.
The application of the octanol/water partition coefficient as logP and the corresponding Hansch pi (.pi.) substituent parameter has been described by Hansch et al., in J. Amer. Chem. Soc., 1964, 86, 1616, J. Amer. Chem. Soc., 1964, 86, 5175, Accts. Chem. Res. 1969, 2, 232, and numerous other subsequent journal articles by these and other authors. Tabulations of the experimentally derived .pi. value for numerous substituents are available in the literature, for example, Hansch et al., J. Med. Chem., 1973, 16, 1207, and Hansch and Leo, "Substituent Constants for Correlation Analysis in Chemistry and Biology", Wiley-Interscience, New York, 1985. Partition coefficients can be calculated by fragment additivity relationships. These calculations are relatively simple for additional methylene units in a hydrocarbon chain, but are more difficult in more complex structural variations. An expert computer program, MEDCHEM, Pomona Medchem Software, Pomona College, California (ver. 3.54), permits consistent calculation of partition coefficients as the log value, clogP, from molecular structure inputs and is used in the present invention to calculate these values.
The concept of the hydrogen bond is widely employed in organic chemistry. The hydrogen bond is a bond between a covalently bonded hydrogen and another atom and is usually represented as A-H . . .B where B is any sigma (.sigma.) or pi (.pi.) electron donor site (Lewis base), referred to as a hydrogen-bond acceptor (HBA), and A in organic compounds is N, P, O, S and Se and is referred to as a hydrogen bond donor (HBD). These bonds are weaker than normal covalent bonds but are well known to stabilize organic chemical structures. Monographs by Joesten and Schaad, "Hydrogen Bonding", M. Decker New York, 1974 and Pimentel and McClellan, "The Hydrogen Bond", Freeman, San Francisco, 1960 discuss various aspects of this subject. Quantitative assessment of hydrogen bonding characteristics for use in structure-activity relationships have been published. Hansch and Leo in "Substituent Constants for Correlation Analysis in Chemistry and Biology", Wiley-Interscience, New York, 1985 give a binomial scale describing hydrogen bond donating and hydrogen bond accepting character for a wide variety of substituent groups. Drago et al. (J. Amer. Chem. Soc., 197 1, 93, 6014) present a double-scale equation for empirically predicting the strengths of the hydrogen bond formation for a variety of pairs of hydrogen bond donors and receivers. This work emphasizes the concept that the strength of the hydrogen bond is dependent on the characteristics of both the hydrogen bond donor and the hydrogen bond acceptor. M. J. Kamlet and R. W. Taft developed an empirical scale defining the hydrogen bond donating (HBD) parameter .alpha. (alpha), and the hydrogen bond accepting (HBA) parameter .beta. (beta). The development of these parameters are described in a series of papers beginning in 1976 (J. Amer. Chem. Soc., 1976, 98, 377 and J. Amer. Chem. Soc., 1976, 98, 2886) and are reviewed in Progress in Physical Organic Chemistry, 1981, 13, 485 and in J. Org. Chem., 1983, 48, 2877. The methods for determining these molecular characteristics and their use in correlating chemical reactions are described in these and other papers in the series. While the parameters .alpha. and .beta. refer to molecular characteristics it is clear from inspection of the tables of values provided in the above reviews that functional group contributions useful in the prediction of hydrogen bonding characteristics can be derived from the molecular values.